Signaling System 7

1
Signaling System 7
2
SS7 - 1

• Common channel interoffice signaling CCIS based
  on SS6
• SS7 developed for ISDN voice and nonvoice
  services
• SS7 is used to set up and manage switch centres
  to provide a range of services

3
SS7 - 2

• Application domestic and international
• Signaling type - digital
• Speed 56/64Kbps
• Link capacity 30K circuits
• Message length lt272 octets
• Routing destination office
• Architecture - layered

4
SS7 - 3

• Flexibility high
• Date of development - mid 70s before OSI
• Messages passed on D channel
• SS7 uses out of band signaling
• SS7 Protocol Architecture Diagram p222

5
SS7 Protocol overview 1

• Message transfer port MTP
• Protocols roughly correspond to the lower three
  layers of the OSI
• Provides physical data link, connectionless
  network functions
• Reliable transfer of signaling messages
• Three layer protocol

6
SS7 Protocol overview 2

• Signaling Connection Control Port SCCP
• Provides some network layer functions, full OSI
  addressing, connection oriented information
  transfer

7
SS7 Protocol overview 3

• User and Application Parts
• Provides end to end signaling functions for
  switched voice and nonvoice services in the ISDN,
  several user parts can operate in parallel over
  single MTP and/or SCCP

8
MTP Level 1 protocol

• Signaling data link OSI physical layer
• Duplex digital links operating at 64Kbps
• Rates 1.55M and 2.048 and 8.448 possible
• USA use 56Kbps

9
MTP Level 2 protocol

• Signaling link OSI data link layer
• Bit oriented protocol
• Detail on p224
• Frames called signaling units
• Begin and end with flag pattern - 01111110
• Zero bit insertion is used for transparency
• Bit stuffing

10
MTP Level 3 protocol

• Signaling network functins lower half of OSI
  network layers
• Functions message handling and network management
  
• Handles routing labels, destination point code
  DPC and origination point code OPC

11
ISDN User Part

• ISUP or ISDN-UP provides signaling for basic ISDN
  circuit-mode bearer services
• Support for voice and nonvoice services
• ISUP provides conectin between two ISDN switches
• Connection identified by circuit identification
  code CIC

12
ISDN User Part

• ISDN call TE sends setup message to the LE on the
  D channel
• LE at originating side siezes a trunk
• Initial address message IAM
• Terminal equipment TE
• Local exchange LE

13
ISDN

• Zero bit insertion is used
• Ref
• ISDN Sec Ed, 1993
• GC Kessler
• McGraw-Hill, ISBN 0-07-034247-4